RELATED ART STATEMENT
1,5-AG is a compound which is present in the cerebrospinal fluid and plasma of humans. It is reported that its quantity is markedly reduced in plasma collected from patients with certain diseases, particularly with diabetes (Yasuo Akanuma, Kazuyuki Tobe, Nippon Naikagakkai Zasshi (Journal of Japanese Internal Medicine Association), 80, 1198-1204, 1991). 1,5-AG is thus expected to be as a marker for diagnosis of diabetes.
As practical assay for 1,5-AG in a specimen, there is known a method which comprises removing sugars present in the specimen other than 1,5-AG, using an ion exchange column chromatography after deproteinization of the specimen; then oxidizing 1,5-AG with pyranose oxidase (hereafter abbreviated as PROD) or L-sorbose PROD) or L-sorbose oxidase and quantitatively determining hydrogen peroxide formed (Japanese Patent KOKAI (Laid-Open) No. 63-185397; hereinafter such a method is referred to as column enzyme method).
Serum or plasma collected from the patient with diabetes is mainly a specimen to be assayed for 1,5-AG. In blood from the patient with diabetes, its glucose concentration is higher than that of normal person. In blood from normal person, the glucose concentration is in the range of approximately 60 to 100 mg/dl, whereas in blood from the patient with diabetes, the glucose concentration is widely distributed in the range of 100 to 1000 mg/dl. On the other hand, the concentration of 1,5-AG in blood is in the range of 1.64 to 2.68 mg/dl for normal person but in the patient with diabetes its concentration is as extremely low as 0.18 to 0.21 mg/dl (Nippon Rinsho (Japanese Clinic), 47, 1989, extra issue, Immunological Inspection in Blood and Urinary Chemical Test over Wide Range; first volume, 439-442, Kawai). Therefore, the concentration of 1,5-AG in blood from the patient with diabetes becomes about 1/470 or less. In addition, glucose is structurally similar to 1,5-AG so that it is impossible to selectively assay for 1,5-AG in the presence of glucose and 1,5-AG in the current state of the art. It is thus essentially required to selectively remove glucose or pretreat specimen by adequately modifying glucose.
In the column enzyme method, proteins and endogenous sugars other than 1,5-AG must be removed and extremely complicated operations for the removal are disadvantageous for the column enzyme method. Furthermore, maltose-added lactate Ringer's solution is often applied as infusion to the patient with diabetes for the purpose of supplementing calorie source, supplementing and compensating for fluid outside tissue in reduced volume of circulated blood and tissue fluid, or correcting metabolic acidosis. In this case, maltose increases in blood of the patient with diabetes. It is reported that maltose present in a specimen collected from such a patient with diabetes cannot be fully removed even by a separation column and hence, there is a serious positive error in measurement data of 1,5-AG ("Rinsho Kagaku (Clinical Chemistry)", 21, 43-48, 1992).